RapWorlds seems pretty cool I guess, I plan to post here plenty...thought I'd refer you to a pretty cool rap forum that just started up called Rhymoholics Anonymous. You can promote and post your music, beats, text, or even better you can battle and post for points and cash. It's really fun, give it a chance and you won't regret it.
Get down there if you can spare some time and represent your skill.http://rhymoholics.com/